Jacquelyn Martin/AP Photo

Sen. Rand Paul, R-Kentucky, held a 13-hour filibuster last year over drones, and he may be preparing to do it all over again.

He said he will filibuster the nomination of David Barron to be a judge for the U.S. Court of Appeals for the First Circuit. Barron's nomination is controversial because of memos he wrote legally justifying the potential use of drone strikes against American citizens.

"I've read David Barron's memos concerning the legal justification for killing an American citizen overseas without a trial or legal representation, and I am not satisfied," Paul said in a statement Thursday. "While the president forbids me from discussing what is in the memos, I can tell you what is not in the memos.

"There is no valid legal precedent to justify the killing of an American citizen not engaged in combat," Paul said. "In fact, one can surmise as much because the legal question at hand has never been adjudicated. Therefore, I shall not only oppose the nomination of David Barron, but will filibuster."

Asked to clarify whether Paul would actually go to the Senate floor to filibuster the speech, Eleanor May, a spokeswoman for Paul, said, "Sen. Paul will do everything in his power to oppose the nomination of David Barron, and thus a filibuster is not out of the question."

Earlier this month, the White House agreed to make Barron's memos available to senators to review ahead of a vote on his nomination.

The nomination of Barron, a Harvard law professor who formerly worked in the Office of Legal Counsel at the Justice Department, may be problematic among some Democrats, as well. Sen. Mark Udall, D-Colo., has said he will oppose the nomination unless the administration makes the drone memos public.

Paul has threatened to place a hold and potentially filibuster several of President Obama's nominees, including Janet Yellen to be chair of the Federal Reserve. He gained notoriety last year when he filibustered John Brennan's nomination to be director of the CIA, asking the White House to explain its justification for drone attacks.

"I rise today to begin to filibuster John Brennan's nomination for the CIA," Paul said in March 2013. "I will speak until I can no longer speak. I will speak as long as it takes, until the alarm is sounded from coast to coast that our Constitution is important, that your rights to trial by jury are precious, that no American should be killed by a drone on American soil without first being charged with a crime, without first being found to be guilty by a court. That Americans could be killed in a cafe in San Francisco or in a restaurant in Houston or at their home in Bowling Green, Kentucky, is an abomination. it is something that should not and cannot be tolerated in our country."

Barron's nomination cleared the Senate Judiciary Committee and will now be considered on the Senate floor. Senate Majority Leader Harry Reid, D-Nevada, invoked cloture on Barron's nomination on Thursday, setting up a potential vote on Barron for as early as Wednesday.